1. Field of the Invention
The present invention relates generally to the art of hydraulic valves used to regulate fluid flow. More specifically, the present invention relates to a valve which controls the flow across the spool opening of a proportional, directional valve as load or system pressures fluctuate.
2. Description of Related Area of Art
Other valves and devices used to control the flow of a fluid have been developed in the past. U.S. Pat. No. 4,361,169 issued to Williams on Nov. 30, 1982 shows a multiple section control valve bank.
Metering and logic elements comprise a control valve section which is connected to a signal chamber designed to change the flow of fluid through the inlet of the valve depending the signals generated from the metering and logic elements. Williams employes a spool and a bore requiring a number of lands and U-shaped passages to generate the proper signals and control characteristics.
U.S. Pat. No. 4,352,375 issued to Williams on Oct. 5, 1982 also discloses a control valve bank. As with the earlier Williams patent, a number of lands are employed along with an intricate heart-shaped flow passage to control fluid flow around a dual supply passage.
U.S. Pat. No. 4,519,419 issued to Petro on May 28, 1985 discloses a hydraulic valve which utilizes a hollow piston having several separate lands with different diameters and various seal diameters.
Finally, U.S. Pat. No. 4,574,839 issued on Mar. 11, 1986 to Yeh, et al discloses a pressure compensated directional control valve. The valve allows the flow rate to a given hydraulic load to be constant regardless of the load imposed and uses a piston mounted within a sleeve valve insert and a number of springs, wherein the piston moves to create a variable orifice to control the hydraulic fluid flow to the load. An adjustable sleeve works in connection with a hollow piston to provide for proper operation of the valve.